Various computer implemented schemes for providing a pseudonym for a user are as such known. A pseudonym is typically used for protecting the informational privacy of a user such as in a social network. Such computer implemented schemes for providing a pseudonym typically enable the disclosure of identities of anonymous users if an authority requests it, if certain conditions are fulfilled. For example, Benjumea et al, Internet Research, Volume 16, No. 2, 2006 pages 120-139 devise a cryptographic protocol for anonymously accessing services offered on the web whereby such anonymous accesses can be disclosed or traced under certain conditions.
A problem occurring in for example social networks is that online communication with another user is always performed with the element of uncertainty that it is not assured that said other user in the online communication is the true user associated with the pseudonym. This problem becomes even more severe in social networks in which absolute user anonymity is desired. There, the pseudonyms of users are selected such as to ensure the anonymity of the user. Hence, an exchange of personal information in order to perform a user authentication is not desired here.